Ground Penetrating Radar refers to the process in which a device radiates short pulses of high-frequency electromagnetic (EM) energy into the ground from a transmitting antenna. When a wave of this EM energy encounters the interface of two different materials (such as an oil tank buried in the ground), a portion of the energy is reflected back to the surface. This reflected energy is detected by a receiver antenna and transmitted to a control unit for processing and display. If the signal does not encounter a buried object the EM signals goes deeper into the ground. The difference between these two readings is what allows us to identify an object buried in the soil.
Short video (2:06 minutes) showing how GPR can be used.
Using ground penetrating radar will give the most accurate results when searching for underground oil tanks. Other devices, while helpful in a search, all have serious limitations which do not allow them to provide the high degree of certainty possible with GPR.